Used as an activated ester in bioconjugation reactions, particularly in the modification of peptides and proteins. It reacts efficiently with primary amines under mild conditions to form stable amide bonds, making it valuable in the synthesis of bioconjugates for pharmaceutical and diagnostic applications. Commonly employed in the preparation of antibody-drug conjugates (ADCs) and labeled biomolecules due to its selective reactivity and compatibility with aqueous buffers. The presence of a protected hydrazine group allows for orthogonal functionalization, enabling sequential conjugation strategies in complex molecule assembly.